Measuring cells of conventionally-known microorganism number-measuring apparatuses have a configuration as follows.
The conventional measuring cell includes a container, a measurement space, a liquid containing space, an agitator, and a measurement electrode. A sampling portion disposed at a lower end of a stick-like specimen-sampling carrier is inserted into the container from a top-surface opening of the container The measurement space and the liquid containing space are sequentially disposed upward from the bottom surface of the container. The agitator is disposed on a basal plane of the measurement space. The measurement electrode is disposed above the agitator in the measurement space. The liquid containing space accommodates a liquid (sample liquid).
In addition, a body of the microorganism number-measuring apparatus is disposed outside the measurement space of the container, and includes a driving unit to drive the agitator. The body performs a measurement of the number of microorganisms by using the measuring cell.
When performing the measurement of the number of microorganisms, after the measuring cell is set in the body of the microorganism number-measuring apparatus, the sampling portion of the stick-like specimen-sampling carrier that has collected microorganisms is inserted into the container of the measuring cell from an upper portion thereof. On this occasion, the sampling portion is disposed in the measurement space disposed in a lower portion of the container, together with the liquid accommodated in the liquid containing space of the container. After that, a driving unit disposed below and outside the container drives to rotate the agitator which is disposed on the basal plane of the measurement space. With the rotation of the agitator, the sampling portion is struck to receive impacts, which thereby releases the microorganisms of the sampling portion into the sample liquid.
The released microorganisms are carried to the measurement electrode by an agitated-water flow of the sample liquid agitated by the agitator. Then, the number of the microorganisms is measured at the measurement electrode.
Note that, after finishing the measurement of the number of microorganisms, a user discards the sampling portion and the sample liquid, together with the measuring cell having the measurement electrode (see, for example, Patent Literature 1 listed below).
In this conventional case, the measuring cell having the measurement electrode is discarded after finishing the measurement of the number of microorganisms, and then a fresh measuring cell is used for the next measurement. Accordingly, since a measurement of the number of microorganisms can always be performed by using a fresh measuring cell, the apparatus has been claimed to be a highly reliable and useful device.
On the other hand, however, in the above conventional case, there has been a problem that it is difficult to prevent improper use of measuring cells.
That is, with a measuring cell once used for measuring, the top-surface of the container thereof remains in an open state for easy removal of the used sample liquid from the measuring cell. Hence, there is a possibility for the user to erroneously consider that the measuring cell would be still useable only if the sample liquid is replaced. Based on the consideration, the user would erroneously reuse the used measuring cell, with the sample liquid thereof being replaced.
However, after having been once used for measurement, the measuring cell is in the state where invisibly small microorganisms remain attached to the measurement electrode thereof, even if the sample liquid has been replaced. For this reason, reuse of the measurement electrode once used for measurement will spoil results of the measurement.